III nitride single crystal, such as aluminum nitride and gallium nitride, has large bandgap energy. Bandgap energy of aluminum nitride is around 6.2 eV, and that of gallium nitride is around 3.4 eV. Bandgap energy of aluminum gallium nitride, a mixed crystal thereof, is between bandgap energy of aluminum nitride and that of gallium nitride according to its component fraction.
Therefore, emission of short-wavelength light in ultraviolet region, which is impossible with the other semiconductor, becomes possible with said aluminum based group III nitride single crystal. And it becomes possible to manufacture light emitting sources such as an ultraviolet-emitting diode for white light source, a disinfectant ultraviolet-emitting diode, a laser available for reading and writing high-density optical disk memory and communication laser. In addition, it can be applied to electronic devices such as ultrafast electron-transfer transistor taking advantage of high saturated drift velocity of electron, and to field emitter taking advantage of negative electron affinity.
For device parts, function as light emitting source, electronic device and the like, it is generally tested to form a multilayered structure wherein thin films thinner than several micrometers are layered on a substrate. These are formed by a well-known crystal growing methods, such as Molecular Beam Epitaxy (MBE) method, Metalorganic Vapor Phase Epitaxy (MOVPE) method and Hydride Vapor Phase Epitaxy (HVPE) method.
As for a substrate forming the above multilayered structure, particularly a multilayered structure which become light-emitting element, a single crystal substrate comprising the above aluminum based group III nitride (Al III nitride, hereinafter), particularly aluminum nitride, is preferable. This is because an influence of lattice mismatch on boundary face or of stress generated by a temperature history when growing can be kept to the minimum, when a single crystal of III nitride, such as aluminum nitride, gallium nitride and the like, or mixed crystals thereof are formed as a growth layer. As a result, it is considered that dislocation density, deficiency and crack in growth layer will be decreased; and emission efficiency will be improved as well. Further, in case when growing ultraviolet-emitting layer, bandgap energy of a substrate part becomes larger than that of emitting layer when Al III nitride single crystal is used as a substrate; accordingly, emitted ultraviolet light will not be absorbed to the substrate and that efficiency of taking out the light will be increased.
Considering manufacturing method of the above Al III nitride single crystal substrate, the present inventors have already proposed a manufacturing method using HVPE method (Patent Articles 1 and Patent Article 2). Said HVPE method is a method wherein III group source gas of III halide gas, such as aluminum trichloride, and nitrogen source gas, such as ammonia, contact a single crystal substrate which is held at an elevated temperature; and then III nitride is epitaxially grown on the single crystal substrate. The method has a feature that crystal growth rate is fast. Accordingly, Al III nitride single crystal can be churned out at a practical level. Therefore, by processing the thick film single crystal obtained on a substrate, such as sapphire, to a wafer-state with the above method, it can be used as an Al III nitride single crystal substrate. Further, by forming multilayered structure on such substrate by a crystal growth method, such as MOVPE method, MBE method and HVPE method, aimed at emission and the like, it is expected that light emitting source is obtainable with high efficiency.
As mentioned above, use of Al III nitride single crystal substrate allow for higher performance and higher quality of growth layer when manufacturing a multilayered structure functional for emission, electron transfer and the like.
Two types of the following devices are conventionally known as a HVPE device for manufacturing a thick-film Al III nitride single crystal. The first type of the device is an integrated type device described in such as Patent Article 1 wherein III group source gas generation part, where Al III halide gas is generated, and a reacting zone, where III group source gas (III group halide) and nitrogen source gas are reacted to grow Al III nitride single crystal on a single crystal substrate, are set in quartz reactor body.
The second type of the device is a separable type device to which a III group source gas generating part is set outside a reactor vessel body, comprising a reacting zone where Al III nitride single crystal is grown on a single crystal substrate; and III group source gas, generated at said III group source gas generating part, is introduced to the reactor vessel body via a pipe. According to the separable type device disclosed in Patent Article 2, III group source gas is made contact with metal aluminum before it is introduced to a reacting zone, removing oxygen impurity.